A comparison of two recent 23-year growth periods in Sphagnum dominated hummocks reveals increased vertical growth and carbon accumulation in ombrotrophic bog, SE Norway

Abstract

Bogs are important sinks of atmospheric carbon (C) due to their unique ability to accumulate vast amounts of partially decomposed litter as peat, containing up to 25% of the world’s soil carbon. Climate change and increases in nitrogen (N) deposition as a result of human activities is expected to affect the dynamics of carbon accumulation and the fate of the carbon sink capacity of peatlands is therefore uncertain. Increased N deposition may alter decomposition dynamics and decrease the carbon sink ability if the layer of peatforming Sphagnum moss becomes N saturated. This study builds on a study by Ohlson and Økland (1998a) who measured peat accumulation variables in an ombrotrophic bog, SE Norway, in 1995. The aim of this study was to collect samples and model peat accumulation in peat that had accumulated since 1995, and compare rates of peat accumulation to those recorded in the previous study. Here I used the exact same location and estimated vertical peat growth, carbon accumulation rate and peat bulk density in Sphagnum dominated hummocks. Peat samples were gathered from the top peat layer and dated using small pines. A subset of samples from hummocks and within the same age-range was then derived from Ohlson and Økland (1998a) to acquire a comparable set of samples. Mean vertical peat growth recorded in 2012 (the current study) was 64% higher compared to the previous measurements, while the mean carbon accumulation rate and bulk density was 85% and 11% higher, respectively. Atmospheric N deposition in the region has decreased the last three decades. Despite this, the mean peat N concentration increased from 1.06% in the previous study, to 1.22% in the samples recorded in 2012. This indicates that the Sphagnum layer is not currently N saturated, and that beneficial climatic conditions might explain the increase in peat growth rates.